1. Field of the Invention
The present invention relates to a photoelectric conversion device. One embodiment of the disclosed invention includes a back contact element structure.
2. Description of the Related Art
A solar cell in which a single crystal silicon substrate or a polycrystalline silicon substrate is used for a photoelectric conversion layer has been developed as one of photoelectric conversion devices. In such a solar cell, an uneven structure is formed on a front surface of the silicon substrate in order to reduce surface reflection. This uneven structure is formed by etching the silicon substrate with an alkaline solution such as NaOH. An alkaline solution has different etching rates depending on crystal plane orientations of silicon. Thus, for example, when a silicon substrate which has a crystal plane orientation of (100) is etched, a pyramidal uneven structure is formed. Back contact solar cells which have such an uneven structure have been proposed (e.g., Patent Document 1 and Patent Document 2).
However, etching with an alkaline solution contaminates a silicon substrate, and thus is not suitable. In addition, etching characteristics greatly vary depending on the concentration or temperature of an alkaline solution, which makes it difficult to form an uneven structure with high reproducibility. In view of the above, a method in which etching with an alkaline solution and a laser processing technique are combined has been proposed (e.g., Patent Document 3).
However, even by the method disclosed in Patent Document 3, it is difficult to form an uneven structure by etching, for example, in the case where a thin film is used as a photoelectric conversion layer.